Damage to an intervertebral disk typically results in abnormal play of the vertebrae contiguous to this disk. This play subjects the posterior articular processes to considerable stresses, generating very painful wear and tear of these processes and general instability of the spinal column. Such instability can also result from an operation performed on a herniated intervertebral disk, which entails access to the disk, thereby weakening the ligament system of the articulation, or can result from certain cases of arthrosis which also subjects the posterior articulations to considerable and painful stresses.
Early implant devices for bracing the spinal column comprise rigid elements which are connected to means of osseous anchoring. The rigid elements frequently consist of metal rods which are implanted along several vertebrae, on either side of the spinous processes. These early devices had the disadvantage of being difficult to implant, and necessitated considerable and complex work in putting them into place. Moreover, they immobilized a relatively long vertebral segment, which significantly reduced the mobility of the patient and subjected the articulations situated on either side of this rigid segment to considerable stresses which often generated new pathological conditions.
Some recently developed interspinous stabilizers are designed to be inserted between the spinous processes. For example, one such stabilizer comprises an interspinous bearing cushion which is fixed to the spinal column by a textile ligament which surrounds the processes. One of the major disadvantages of the bearing cushion is being relatively rigid and holding the vertebrae in a specific position, thereby creating discomfort for the patient. In addition, the bearing cushion tends to wear under the influence of repeated stresses to which it is subjected.
Other relatively recent interspinous stabilizers have anchoring members, which are adapted to be attached to processes, directly perpendicular to a spring body that provides stability during extension. These interspinous stabilizers, while helpful in limiting the range of spinal motion during extension, lack sufficient support in flexion and thus may create a flat back or kyphotic positioning in the spine. Moreover, these interspinous stabilizers may produce an undesirable load environment at adjacent spine levels.
Therefore, there is a need for interspinous stabilizers that can provide stability during both flexion and extension.